Concentrations Of Al2O3 Nanoparticles Research Articles

Математична модель тепломасообміну в каналі з нанорідиною при його нерівномірному нагріві концентрованим тепловим потоком

This work is aimed at determining the expediency of using a nanofliud (a special suspension with nanoparticles) as a heat transfer agent for a parabolic trough solar plant. Adding nanoparticles to a base heat transfer agent intensifies convective heat exchange inside the channel, thus increasing the total heat efficiency of the receiver system. A refined nonlinear 3D mathematical model was developed to study heat-and-mass transfer in the receiver system of a parabolic trough solar plant that consist of a concentrator and a tube heat receiver with a nanofluid. In the mathematical model, the values of the nonuniform heat flux on the tube heat receiver surface are found by approximating numerical data obtained by the Monte Carlo method. This simplifies the classical coupled deterministic-statistical mathematical model and allows one to obtain a purely deterministic model solved by the finite volume method. The model also accounts for the thermal conductivity of the heat receiver wall, the actual ambient conditions, and the heat loss from the heat receiver surface. A numerical algorithm was developed to conduct numerical parametric studies on determining the temperature fields of Syltherm800/Al2O3 nanofluid heat transfer agent. This nanofluid is prepared from the traditional heat transfer agent of parabolic trough solar plants – Syltherm800 silicone oil – by adding aluminum oxide nanoparticles thereto. The numerical studies were conducted both for pure Syltherm800 oil and for Syltherm800/Al2O3 nanofluid with an Al2O3 nanoparticle concentration of 3, 5, and 8 per cent. This study is the first to find that the use of a nanofluid as a heat transfer agent for a parabolic trough solar plant produces a positive effect only in the case of the laminar flow of a nanofluid heat transfer agent with a high nanoparticle concentration. A verification of the obtained numerical data showed that they are in satisfactory agreement with experimental ones.

Mechanical and Thermal Properties of Aluminum Matrix Composites Reinforced by In Situ Al2O3 Nanoparticles Fabricated via Direct Chemical Reaction in Molten Salts

The development of novel methods for industrial production of metal-matrix composites with improved properties is extremely important. An aluminum matrix reinforced by “in situ” α-Al2O3 nanoparticles was fabricated via direct chemical reaction between molten aluminum and rutile TiO2 nanopowder under the layer of molten salts at 700–800 °C in air atmosphere. Morphology, size, and distribution of the in situ particles, as well as the microstructure and mechanical properties of the composites were investigated by XRD, SEM, Raman spectra, and hardness and tensile tests. Synthesized aluminum–alumina composites with Al2O3 concentration up to 19 wt.% had a characteristic metallic luster, their surfaces were smooth without any cracks and porosity. The obtained results indicate that the “in situ” particles were mainly cube-shaped on the nanometer scale and uniform matrix distribution. The concentration of Al2O3 nanoparticles depended on the exposure time and initial precursor concentration, rather than on the synthesis temperature. The influence of the structure of the studied materials on their ultimate strength, yield strength, and plasticity under static loads was established. It is shown that under static uniaxial tension, the cast aluminum composites containing aluminum oxide nanoparticles demonstrated significantly increased tensile strength, yield strength, and ductility. The microhardness and tensile strength of the composite material were by 20–30% higher than those of the metallic aluminum. The related elongation increased three times after the addition of nano-α Al2O3 into the aluminum matrix. Composite materials of the Al-Al2O3 system could be easily rolled into thin and ductile foils and wires. They could be re-melted for the repeated application.

Machining feasibility and Sustainability study associated with air pressure, air flow rate, and nanoparticle concentration in Nanofluid minimum quantity lubrication-assisted hard milling process of 60Si2Mn steel

In recent years, more efficient hard machining processes have notably increased in demand for higher productivity but environmental friendliness. High hardness and strength as well as the enormous amount of cutting temperature are still the biggest obstacles. Nanofluid minimum quantity lubrication (NFMQL)–assisted hard machining has become a feasible and promising solution to overcome these problems. The work presents the experimental study on the effects of air pressure (5, 6, and 7 bar), air flow rate (150, 200, and 250 L/min), and Al2O3 nanoparticle concentration (0.5, 1.0, and 1.5%) on minimum quantity lubrication (MQL) hard milling process of 60Si2Mn (50÷52HRC) using vegetable oil as the based fluid. Box–Behnken experimental design and ANOVA analysis were employed to investigate the influences and interaction effects of input parameters on cutting forces, surface roughness, and surface microstructure. This study will be used for selecting the optimum air pressure, air flow rate, and Al2O3 nanoparticle concentration for efficient cooling lubrication performance of MQL in sustainable hard machining. The obtained results show that the optimal values for air pressure and nanoparticle concentration. For Q = 200 L/min, the optimal p is 6.0 bar and the optimal nanoparticle concentration (NC) is 0.9%. For Q = 250 L/min, the optimal p is 5.2 bar, and the optimal NC is 1.2%. Furthermore, using air flow rate Q = 250 L/min gives better results than Q = 200 L/min, but the selection will be depended on the specific equipment conditions.

Experimental investigation of increasing heat transfers inside a double pipe heat exchanger by using Al2O3 nanofluid

The aim of the present study is to investigation of increasing of the heat transfer coefficient inside the double tube. This is done by mixing water with aluminum oxide nanoparticles (Al2O3), the study was carried out experimentally. In this study, the effects of nanofluids at different volume concentrations from 0.05% to 0.4%, different mass flow rates of the nanofluids inside the tube, and different mass flow rates of the water flow through the annulus were tested. Experiments done with different nanoparticles and without nanoparticles under the same operating conditions. The experiment was designed, and built in the laboratory according to the international specifications and standards of the tubular exchanger manufacturers association (TEMA). By collecting and analyzing the results of the experiments, it was found that the nanoparticles have a significant improvement in the heat transfer coefficient inside the double tube. The heat transfer coefficient inside the tube increases with the increase the Reynolds number of the tube flow. The maximum value of the Nusselt number is when the volume concentration of Al2O3 nanoparticles is 0.1%.

Experimental investigation of a two-phase closed thermosyphon with Al2O3/R134a nanorefrigerant

Nanorefrigerants are mixtures of refrigerant and nanoparticles, which enhance the heat transfer in both air-conditioning and refrigeration systems. In the present work, the nanorefrigerant Al2O3/R134a is applied in a two-phase closed thermosyphon in order to investigate its thermal performance. More specifically, the influence of the Al2O3/R134a on the thermal resistance and heat transfer coefficient for various heat inputs in a two-phase closed thermosyphon were investigated experimentally. The two-phase closed thermosyphon was tested by varying the concentration of Al2O3 nanoparticles from 0.5% up to 1.5% by weight basis in the usual refrigerant R134a. The results of the experimental investigations indicate that there is a significant enhancement in heat transfer by 93.2% when the nanoparticle concentration of 1.0% was used in R134a when compared to the thermosyphon tested with pure R134a. The nanorefrigerant in thermosyphon has reduced its thermal resistance significantly by 59%. The heat transfer coefficient obtained for nanorefrigerants in two-phase closed thermosyphon is validated by Cooper correlation. It is inferred from the study that the depositions of nanoparticles in the thermosyphon enhance heat transfer. A new correlation to predict the rate of heat transfer is also proposed for employing the nanorefrigerants in a two-phase closed thermosyphon. The predicted correlation, heat transfer coefficient and thermal resistance are optimized by using Grey Relation analysis by computing the grade between the minimum and maximum values obtained from the experimental results.

Synthesis and Characterization UV-Curable Waterborne Polyurethane Acrylate/Al2O3 Nanocomposite Coatings Derived from Jatropha Oil Polyol

A new UV-curable waterborne polyurethane acrylate/alumina (UV-WPUA/Al2O3) coatings were successfully developed. The waterborne polyurethane acrylate (WPUA) dispersion was synthesized by reacting jatropha oil polyol (JOL) with isophorone diisocyanate (IPDI), 2,2-dimethylol propionic acid (DMPA), and 2-hydroxyethyl methacrylate (HEMA) via in-situ and anionic self-emulsifying methods. The WPUA/Al2O3 dispersion was formulated by various sonicating concentrations of alumina nanoparticles (0.3, 0.6, 0.9, and 1.2 wt%) into WPUA dispersion. The UV-WPUA/Al2O3 coatings were obtained with 75 wt% oligomers, 25 wt% monomer trimethylolpropane triacrylate (TMPTA), and 3 wt% of a commercial photoinitiator (benzhophenol) for UV-curing were used. The effect of Al2O3 nanoparticles on WPUA coatings was analyzed by FTIR, surface morphology, and coating performance properties such as pendulum hardness, pencil hardness, scratch resistance, and adhesion test. FTIR revealed the formation of JOL, neat UV-WPUA, and UV-WPUA/Al2O3 coatings, respectively. FESEM/EDX demonstrated that Al2O3 nanoparticles at the lower loading (up to 0.6 wt%) were well-dispersed correlated with contact angle (CA). The hardness property can reach 63.4% at the lower concentration of the Al2O3 addition 0.6 wt%. The adhesive strength, scratch hardness, and scratch resistance were greatly improved to 5B, 5H, and 2N, respectively. The preparation method offered in this study is an effective and convenient approach to producing UV-WPUA/Al2O3 coatings. The enhancement of the properties with the lesser concentration of Al2O3 nanoparticles (≤ 0.6 wt%) addition in this study shows a new promising potential as surface coating application for several major industrial areas, such as marine, transportation, and biomedical field with major economic and environmental benefits.

Flow and heat transfer characteristics of a nanofluid as the coolant in a typical MTR core

Abstract The purpose of this work was to perform a thermal–hydraulic numerical analysis of a nanofluid as the coolant in a typical MTR (material testing reactor) core. Numerical simulation was carried out for turbulent flow of water based nanofluid of different concentrations of Al2O3 nanoparticles through a sub-channel of a typical MTR core subjected to cosine shape heat flux at various values of Reynolds number using the Ansys-Fluent computer code. The optimum performance of the studied nanofluid as a coolant in MTR core was determined by the determination of the conditions under which the total entropy generation due to both heat transfer and fluid flow had a minimum value. The results showed that this condition was at Re = 4.8 × 104. The studied range of Reynolds number (Re) and particle concentration (ϕ) were 2.5 × 104 ≤ Re ≤ 5.6 × 104 and 0% ≤ ϕ ≤ 9% respectively. Results for local and average heat transfer and flow characteristics were presented. For the studied range of Reynolds number and particle concentration, four new correlations were developed. Two correlations relating Nusselt number and friction coefficient with the parameters Re and ϕ whereas the other two correlations were one relating Nusselt number with Reynolds and Prandtl numbers and the other relating the friction coefficient with Reynolds number.

Entropy analysis of thermally radiating MHD slip flow of hybrid nanoparticles (Au-Al2O3/Blood) through a tapered multi-stenosed artery

This paper deals with the heat transfer and entropy generation analysis of unsteady blood flow through a tapered multi-stenosed artery incorporating hybrid nanoparticles (gold and alumina) with Joule heating, viscous dissipation, radiation, and inclined magnetic field. For the realistic behavior of blood, Reynold’s viscosity model is considered in this study. The Crank-Nicolson scheme is applied to solve the continuity, momentum, and energy equations with appropriate initial and boundary conditions. The important findings are represented graphically and have been analyzed for different values of the dimensionless parameters. The velocity contours for several emerging parameters are presented to study the overall behavior of blood flow patterns. It is observed that the axial flow accelerates with increasing wall slip velocity (ws) due to the presence of the hydrodynamic wall slip effect. The velocity profile increases as the concentration of Au nanoparticles increases, while the reverse effect is noted for the concentration of Al2O3 nanoparticles. The current findings may be helpful for biomedical scientists who are interested in investigating the treatment of various cardiovascular diseases.

THERMAL-HYDRAULIC PERFORMANCE OF Al2O3 NANOFLUIDS UNDER LAMINAR FLOW IN A MINITUBE

The improvement of performance and applications that include the convection heat transfer process is extremely related to the thermophysical properties of the fluids. However, it was found that adding nanoparticles to the conventional fluids (known as nanofluids) is an advanced way to enhance their thermophysical properties leading to an enhanced heat transfer process. This study presents a numerical approach to investigate the laminar flow-based convective heat transfer of Al2O3 nanofluids in a mini-tube under constant heat flux boundary conditions (15 kW/m2) and at an inlet temperature of 25°C. For this study, the nanofluid samples are prepared for several concentrations of Al2O3 nanoparticles and ethylene glycol/water mixture as a base fluid. Also, the thermal properties of nanofluids and base fluid are characterized. Computational fluid dynamics tools are used to develop a numerical model and validate it in comparison to experimental data. The results are discussed based on the heat transfer coefficient, considering the entrance area, pressure drop, and friction factor to determine the performance of nanofluids in comparison to the base fluid. A considerable enhancement in the heat transfer, especially in the entrance area up to 17.8%, with a corresponding increase in the pressures drop, friction factor, and the required pumping power of the nanofluids was observed.

Forced convection heat transfer characteristics of Al2O3 nanofluids in a minichannel - an experimental study

In this study, an experimental investigation on the convective heat transfer characteristics of Al2O3 nanofluids flowing through an horizontal minichannel under the laminar and turbulent flow and constant heat flux conditions is performed. Several sample nanofluids were prepared using two base fluids (water and the mixture 80/20 DW/EG vol.%) and several low concentrations of Al2O3 nanoparticles ranging from 0.01 to 0.1 vol%. An existing experimental setup was modified for this study. The measurements were taken for the base fluid and nanofluids at each flow and heating conditions. The results are analyzed in terms of Nu and friction factor (f) in comparison with those of the base fluid. The results demonstrate that the used low concentrations of Al2O3 nanoparticles are not enough to yield any noticeable enhancement in heat transfer of the nanofluid samples. The deviations between the results of the nanofluids and the base fluid are small and within the uncertainty range of the experimental setup.

Performance of Sprayed PVDF-Al2O3 Composite Coating for Industrial and Civil Applications

Because of their great water repellency, Superhydrophobic coatings have a major impact on a variety of industrial applications. The current study’s key originality is the development of low-cost, stable, superhydrophobic, and corrosion-resistant composite coatings. In the present work, polyvinylidene fluoride (PVDF)/Al2O3 composite coatings were produced using the spray technique to investigate the wettability and corrosion behavior of the coated materials for industrial and civil applications. PVDF was mixed with various concentrations of Al2O3 nanoparticles, and the mixture was sprayed onto steel, aluminum, and glass substrates. The wettability and morphology of the coated surfaces were investigated using the sessile droplet method and scanning electron microscopy, respectively. The corrosion resistance of bare substrates was compared to that of those coated with PVDF alone and those coated with PVDF/Al2O3 nanoparticles using Tafel polarization techniques. The force of adhesion between the coat and the substrates was measured in pounds per square inch. A nanoindentation test was also used to measure the hardness of the coating layer. The PVDF/Al2O3 coated steel showed a significantly higher water contact angle and lower contact angle hysteresis, reaching 157 ± 2° and 7 ± 1°, respectively, compared to the coated aluminum and glass substrates. Corrosion test results showed that the superhydrophobic PVDF/Al2O3 coatings had a much higher corrosion protection efficiency for steel and aluminum than that of the PVDF ones. The PVDF/Al2O3 coated substrates showed moderate but still acceptable adhesion between the coating layer and the substrates. Moreover, the PVDF/Al2O3 coatings had much better mechanical properties than the PVDF only coatings. Such type of coating could be a promising candidate for possible industrial and civil applications.

Effect of Concentration of Al2O3 Nanoparticles on Electrical Properties of Mineral Oil

This study aimed to compare the electrical characteristics of mineral oil-based nanoparticles to those of pure mineral oil. Mineral oil used in distribution transformers was mixed with aluminum oxide (Al2O3) nanoparticles, which serve as an insulator, with 0.01, 0.03, and 0.05 % mineral oil volume concentrations. The moisture content in mineral oil was measured beforehand, and the electrical tests were subsequently conducted in accordance with international standards. The moisture content test revealed that the combination of nanoparticles and mineral oil resulted in an increase in moisture content. As regards the test of AC withstanding voltage and negative polarity lightning impulse voltage, it was found that the mineral oil mixed with the nanoparticles had higher dielectric strength than the original mineral oil. In addition, the test results of positive polarity lightning impulse voltage demonstrated that with a mixture of mineral oil and the nanoparticles at a 0.01 % concentration, the positive polarity lightning impulse dielectric strength of the mineral oil increased. However, at concentrations of 0.03 and 0.05 %, it did not rise, regardless of the increasing volume of nanoparticles. The results, thus, showed promising directions for applications of nanoparticles in the development of electrical properties of mineral oil. HIGHLIGHTS The addition of Al2O3 nanoparticles to the mineral oil resulted in an increase in the oil moisture content. However, it was found that the moisture content in the mineral oil tended to decrease with the increase in the amount of nanoparticles The optimum nanofluid combination in terms of increased AC breakdown strength was created by adding Al2O3 nanoparticles to mineral oil at a rate of 0.05 vol% The Al2O3 nanoparticles being added to the mineral oil can give an increase in the impulse breakdown voltage with the negative polarity For the positive polarity of the impulse breakdown voltage, the best nanofluid mixture in terms of increased breakdown strength was produced by the addition of Al2O3 nanoparticles at a rate of 0.01 vol% to the mineral oil GRAPHICAL ABSTRACT

Nucleate pool boiling enhancement with the application of a hybrid technique involving the addition of alumina nanoparticles to stirred water above heating surface

The nucleate boiling heat transfer coefficient (HTC) can be improved using either active or passive techniques. According to the present disclosure, both techniques are used in combination. In the passive technique, nanoparticles are added to water, whereas a rotating mixer is used in the active technique to improve the boiling HTC of pure water. This study uses hybrid techniques for HTC enhancement at nucleate pool boiling regime. Experiments were carried out using circular brass as a horizontal heating surface. Different concentrations of Al2O3 nanoparticles were tested. The rotation speed of the mixer varied at 0, 350, 600, and 800 rpm. This combined technique resulted in 58.8% enhancement in HTC at 280 kW/m2 heat flux and 0.03% nanoparticle concentration. By comparison, the HTC was enhanced by 23.6% when nanoparticles were added without a mixer, whereas the enhancement ratio was 27.1% when a mixer was used in the absence of nanoparticles under the same conditions.

Effects of different concentrations of Al2O3 nanoparticles and base fluid types on pool boiling heat transfer in copper foam with bottom condensed reflux

A closed-loop type experimental system of pool boiling heat transfer with condensed reflux in the bottom was developed to study the boiling heat transfer of copper foams in different working fluids, including deionized water, water-based Al2O3 nanofluids, ethylene glycol/deionized water mixed fluid and ethylene glycol/deionized water-based Al2O3 nanofluids. The pore densities of copper foams are 5, 30 and 60 pores per inch (PPI) and the foam thickness are 2, 4, 6 and 8 mm, while the porosity remains a fixed value of 0.9. Al2O3 nanoparticles with an average diameter of 50 nm are used in this study and their mass concentrations are 0.01%, 0.05% and 0.1%. The results show that the concentrations and types of nanofluids and the structural parameters of copper foams have significant effects on the boiling heat transfer performance. Introducing the condensed reflux back to the bottom of boiling chamber can enhance the boiling heat transfer performance compared with the conventional pool boiling experimental condition. Under the current experimental settings, the gravity-capillary driven condensed reflux can offer extra liquid replenishment to the copper foam surface, improving the rewetting ability and therefore enhancing the boiling heat transfer. In addition, the scouring effect of condensed reflux can promote the bubble departure and decrease the bubble release resistance, and inhibit the deposition of nanoparticles on the heating surface.

Tribological Properties of Al2O3 Nanoparticles as Lithium Grease Additives

The tribological properties of Lithium grease specimens with different concentrations of Al2O3 nanoparticles were investigated using a pin on disc apparatus under different sliding speeds and normal loads. Results showed that Al2O3 nanoparticles enhanced the tribological properties of lithium grease and reduced the COF and wear scar width by approximately 57.9% and 47.5% respectively.

Evaluating the Toxicity and Histological Effects of Al2O3 Nanoparticles on Bone Tissue in Animal Model: A Case-Control Study.

The applications of nanostructures have been limited by their different toxicities. So, the investigation of these toxicities is necessary before nanostructure application. This study aimed to evaluate the effect of aluminum oxide (Al2O3) nanoparticles on bone density in Wistar rat. Al2O3 nanoparticle was prepared by the sol-gel method. Characterization was done by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Sixty-four male adult Wistar rats were divided into eight groups including six groups intravenously treated with Al2O3 nanoparticle at concentrations of 25, 50, 100, 250, 500, and 1000 µg/ml: one group received food and water as the control group, and one group received food and water as well as intravenously distilled water as an injection control group. After 41 days, bone density was analyzed by dual-energy X-ray absorptiometry (DEXA). According to X-ray diffraction, the average particle size for Al2O3 nanoparticles was 20.85 nm. The data of densitometry showed that the bone density of right and left foot was reduced in concentrations of 250, 500, and 1000 µg/ml that were statistically significant in comparison with the control group. The reduction of bone density was increased with the enhancement of nanostructures concentration. The effect of Al2O3 nanoparticles on bone density was similar in the left and right legs. Histopatholological assessment also showed that Al2O3 nanoparticles (250, 500, and 1000 µg/ml) lead to significant reduction of trabeculae. Empty lacunae are observed in these three groups. Considering that high concentrations of Al2O3 nanoparticles had toxicity on bone tissue, it must be used by more caution, especially its use as a coating in different devices such as implants, surgical instruments, and bone prostheses.

Heat transfer performance of a nanofluid-filled tube with wall corrugations and center-cleared twisted-tape inserts

ABSTRACT We numerically examine the thermal performance of a round tubular heat exchanger featuring a combination of three passive techniques for heat-transfer enhancement: (i) center-cleared twisted-tape inserts, (ii) tube corrugations, and (iii) nanofluids. We consider three geometric tape parameters – the central-clearance width (C), the tape width (W), and the 180° tape pitch (H) – across a range of Reynolds numbers (500 ≤ Re ≤ 1250). For both water and a representative nanofluid (Al2O3-water), increasing W or decreasing C or H is found to increase the heat transfer coefficient at all Re. Switching from water to one of four water-based nanofluids − Al2O3-water, CuO-water, Cu-water, and TiO2-water – is found to improve the heat transfer rate sufficiently to overcome any associated rises in pressure drop, resulting in thermal efficiencies higher than those of water. The highest thermal efficiency coefficient (η = 1.157) occurs with the Cu-water nanofluid at the smallest Re (500), whereas the lowest thermal efficiency coefficient (η = 1.115) occurs with the CuO-water nanofluid at the largest Re (1250). Across the entire Re range, increasing the volume concentration of Al2O3 nanoparticles (from ϕ = 2 to 5%) is found to increase the coefficients of heat transfer and thermal efficiency. This study provides new insight into how the heat transfer capabilities of a tubular heat exchanger can be enhanced by combining center-cleared twisted-tape inserts, tube corrugations and nanofluids.

Experimental investigation of parallel type -evacuated tube solar collector using nanofluids

ABSTRACT The utilization of fossil fuels can be minimized by the application of solar energy. In this paper, the performance of Parallel-Type (PT) Evacuated Tube Solar Collectors (ETSC) using Al2O3 nanofluid was experimentally investigated. The solar collector was used during both the on-peak and off-peak periods. As a result, the efficiency of the ETSC was calculated by adding various range of particle concentration of Al2O3 nanoparticles in the base fluid. The circulating fluid with flow rates of 0.035 and 0.065 kg/sec. The maximum efficiency procured as of the solar collector at a flow rate 0.035 kg/sec with concentrations of 0.1, 0.2, and 0.3 vol% of Al2O3 nanofluid was 61.8%, 65.4%, and 69.5%, respectively. An improvement of 6.7%, 7%, and 7.7%, efficiency was achieved compared to the flow rate of 0.065 kg/sec. The most optimal concentration of 0.3vol% Al2O3 nanofluid shown progress in thermal efficiency compared to other percentage of nanofluid and water. Improvisation of efficiency by incorporating the Al2O3 nanoparticles in the base fluid in the evacuated tube solar collector. Withal, the investigation includes the prognostication of temperature at entry and exit fluid, solar radiation, ambient temperature, energy output, and also the collector efficiency. Moreover, the investigation was focused toward the evaluation of the efficiency in PT-ETSC at various condition of the environment. Finally, based on the test results, present work could be recommended for agriculatural purpose specifically in vegitable drying conditions.

Experimental investigation on solar flat plate collector using alumina nanofluid with tube inserts

ABSTRACT The heat transfer and friction characteristics of thermosyphon solar flat plate collector using Al 2 O 3 /water nanofluid as working fluid with helical twist insert and its impacts are analysed. Thermal behaviour, heat augmentation and pressure drop characteristics of the modified collector are compared with those of conventional riser tube collector. Alumina nanofluid of 0.1%, 0.3% and 0.5% volume concentrations are used in riser tube of the solar flat plate collector which has helical twist with rod as insert. Correlations for heat augmentation and friction factor in terms of performance parameters like Nusselt number, Prandtl number and fluid concentrations showed acceptable deviations. The convective heat transfer coefficient varies directly with the volume concentration of Al2O3 nanoparticles in base fluid, conversely increasing the fluid concentration increase the density of the nanofluid leading to increase in pressure drop and friction. Results favour to modified nanofluid collector in terms of thermal performance, higher heat removal rate from absorber plate in solar flat plate collector.

Numerical study on forced convection of water-based suspensions of nanoencapsulated PCM particles/Al2O3 nanoparticles in a mini-channel heat sink

The contributions of Al2O3 nanoparticles and nanoencapsulated PCM particles for enhancing the heat transfer in the rectangular mini-channel heat sink are compared in this work. A three-dimensional numerical method is used to simulate the forced convection heat dissipation of water-based suspensions of nanoencapsulated PCM particles/Al2O3 nanoparticles in the mini-channel heat sink. A homogenous mixture formulation by means of the pseudo-vorticity-velocity formulation together with the energy equation is adopted to evaluate the cooling characteristics. Several important factors in the system such as the friction factor, the thermal resistance, the figure of merit, and the average heat transfer coefficient ratio are investigated at various concentrations of Al2O3 nanoparticles and nanoencapsulated PCM particles, flow Reynolds numbers, and heat fluxes. The numerical results clearly reveal that the maximum thermal resistance reduction of 1.2% and 6.9% can be observed by adding the nanoencapsulated PCM suspension with the concentrations of 2% and 10%, respectively. For the case of water-based suspension of Al2O3 nanoparticles, the heat transfer coefficient ratios are larger than unity for all values of heat flux and Reynolds number. The usage of Al2O3 nanoparticles provides better cooling performance as compared with the case of nanoencapsulated PCM particles. As a result, the beneficial effect of Al2O3 nanoparticles is much greater as compared with that of nanoencapsulated PCM particles.